1. Field of the Invention
The present invention relates to an antenna board which is formed by laminating dielectric layers and conductor layers.
2. Description of Related Art
As indicated by the cross-sectional view and top view shown in FIGS. 14A and 14B, respectively, and the exploded perspective view shown in FIG. 15, for example, an antenna board includes a dielectric board 11 in which a plurality of dielectric layers 11a to 11e are laminated, a ground conductor layer 12 for shielding, a strip conductor 13 for inputting and outputting high-frequency signals, and a patch conductor 14 for transmitting and receiving electromagnetic waves.
The dielectric board 11 is, for example, formed by the five layers of the dielectric layers 11a to 11e being laminated vertically. The dielectric layers 11a to 11e are formed by, for example, a resin layer with glass cloth and a resin without glass cloth. The ground conductor 12 is deposited on the entire bottom surface of the dielectric layer 11a located on the bottom layer. The around conductor 12 includes, for example, copper. The strip conductor 13 is opposed to the ground conductor 12 across the dielectric layer 11a, and is disposed between the dielectric layers 11a and 11b. The strip conductor 13 is a narrow strip-shaped conductor extending in one direction from the outer peripheral edge to the central part in the inner part of the dielectric board 11, and includes an end part in the central part of the dielectric board 11. The strip conductor 13 includes, for example, copper.
The patch conductor 14 includes a first patch conductor 14a, a second patch conductor 14b, and a third patch conductor 14c. These patch conductors 14a to 14c have quadrangle shapes. The patch conductors 14a to 14c include, for example, copper.
The first patch conductor 14a is disposed between the dielectric layers 11c and 11d so as to cover the position of the end part 13a of the strip conductor 13. The first patch conductor 14a is connected to the end part 13a of the strip conductor 13 via a penetration conductor 15 penetrating the dielectric layer 11c and a penetration conductor 16 penetrating the dielectric layer 11b. 
The second patch conductor 14b is disposed between the dielectric layers 11d and 11e so as to cover the position where the first patch conductor 14a is formed. The second patch conductor 14b is electrically independent. The third patch conductor 14c is disposed on the top surface of the dielectric layer 11e so as to cover the position where the second patch conductor 14b is formed. The third patch conductor 14c is electrically independent.
In this antenna board, when a high-frequency signal is supplied to the strip conductor 13, the signal is transmitted to the first patch conductor 14a via the penetration conductors 15 and 16. The signal is radiated as an electromagnetic wave to the outside via the first patch conductor 14a, the second patch conductor 14b and the third patch conductor 14c. By the way, the reason why the antenna board like this includes the electrically independent second patch conductor 14b and third patch conductor 14c as well as the first patch conductor 14a is that the bandwidth of the frequency band of the antenna can be widened by such a configuration. Such a conventional antenna board is described, for example, in Japanese Unexamined Patent Application Publication No. H5-145327.
However, for example, in the wireless personal area network, the frequency band to be used is different in each country, and it is required to cover the wide frequency band so that one antenna board is usable in the whole world. To achieve this, an antenna board with a frequency band further wider than the conventional antenna board is required to be provided.